Generally, a vehicle is provided with a passenger protecting system for protecting passengers in a collision of the vehicle. The passenger protecting system has, for example, an airbag device for deploying an airbag to protect the head portion or the like of the passenger, and/or a pre-tensioner device for taking up a slack of a seat belt of the vehicle.
The airbag device and the pre-tensioner device are controlled by a control unit such as an ECU. The ECU performs a determination of the vehicle collision based on signals from sensors mounted to the vehicle, and actuates the airbag device and the pre-tensioner device when the vehicle collision is determined.
It is desirable for the passenger protecting system to protect the passenger not only from a vehicle collision in the vehicle traveling direction (i.e., vehicle front-rear direction), but also from a side collision of the vehicle which causes a vehicle-width-direction impact on the vehicle. For example, as disclosed in JP-2-249740A, the airbag device for protecting the passenger from the side collision of the vehicle is provided with a side airbag, which can be deployed according to detection signals of a pressure sensor. The pressure sensor detects a pressure of an inner space of the vehicle door.
Generally, a pressure sensor is provided with a case member in which a sensing unit of a circuit assembly for detecting the pressure is housed, and a passage member defining therein a pressure introduction passage through which the pressure is transferred to a detection surface of the sensing unit. The pressure introduction passage is communicated with the interior of the case member, and has a lower opening portion which is opened downward to be communicated with the exterior of the case member.
Because a circuit board or the like of the circuit assembly which is accommodated in the case member will malfunction due to wetting, the case member is required to have a high watertightness performance. That, liquid is to be restricted from entering the case member except the detection surface, which faces the pressure introduction passage communicated with the exterior.
In this case, the lower opening portion of the pressure introduction passage is opened downward, to restrict liquid and foreign matter from attaining the sensing unit.
However, when liquid such as rain intrudes into the pressure introduction passage through the lower opening portion so that the pressure introduction passage is blocked, the upper space of the pressure introduction passage will become a closed space. Because the gravity of the liquid is counterbalanced due to a pressure decrease of the closed upper space, the liquid is hampered from flowing downward (i.e., from being discharged from pressure introduction passage). Particularly, in the case where the liquid is solidified due to a temperature decrease or the like, the transference of the pressure of the exterior to the detection surface is impaired. Therefore, the reliability of the pressure sensor is lowered.